Method for growth of atomic layer ribbons and nanoribbons of transition metal dichalcogenides

ABSTRACT

A method of making an atomic layer nanoribbon that includes forming a double atomic layer ribbon having a first monolayer and a second monolayer on a surface of the first monolayer, wherein the first monolayer and the second monolayer each contains a transition metal dichalcogenide material, oxidizing at least a portion of the first monolayer to provide an oxidized portion, and removing the oxidized portion to provide an atomic layer nanoribbon of the transition metal dichalcogenide material. Also provided are double atomic layer ribbons, double atomic layer nanoribbons, and single atomic layer nanoribbons prepared according to the method.

BACKGROUND

Atomically-thin (i.e., two-dimensional) materials such as graphene andtransition metal dichalcogenides (TMDs) have triggered tremendousinterest in both fundamental science and practical applications becauseof their reduced dimensions, which provide intriguing physical andchemical properties and thereby unique applications. In particular,ribbons and nanoribbons of TMDs, with an additional space confinement inthe two-dimensional plane (i.e., ribbon-like morphologies, generallywith a length-to-width ratio of greater than 1000) and a more prominentedge effect compared to two-dimensional sheets, have the potential toprovide even more unprecedented properties according to theoreticalpredictions. Therefore, synthesis and fabrication approaches forproviding atomically-thin TMD ribbons and nanoribbons are highlydesired.

SUMMARY

The present disclosure is directed to a method of preparing atomic layerribbons and nanoribbons of a TMD material. According to some aspects,the method comprises forming a double atomic layer ribbon comprising afirst monolayer and a second monolayer positioned on a surface of thefirst monolayer, and removing at least a portion of the double atomiclayer ribbon to provide an atomic layer nanoribbon of a TMD material asdescribed herein. The present disclosure is also directed to doubleatomic layer ribbons and nanoribbons, and single atomic layernanoribbons, prepared according to the methods as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example schematic of the CVD growth in the methodaccording to the present disclosure.

FIG. 2A shows an example double atomic layer ribbon according to aspectsof the present disclosure.

FIG. 2B shows an example cross-sectional view of the double atomic layerribbon of FIG. 2A

FIG. 3A shows an example double atomic layer ribbon according to aspectsof the present disclosure.

FIG. 3B shows an example cross-sectional view of the double atomic layerribbon of FIG. 3A.

FIG. 4A shows an example double atomic layer nanoribbon of a TMDmaterial according to aspects of the present disclosure.

FIG. 4B shows an example cross-sectional view of the double atomic layernanoribbon of FIG. 4A.

FIG. 5A shows an example cross-sectional view of a double atomic layerribbon according to aspects of the present disclosure.

FIG. 5B shows an example cross-sectional view of a single atomic layernanoribbon according to aspects of the present disclosure.

FIG. 6A shows a scanning electron microscopy (SEM) image of the doubleatomic layer ribbon prepared according to Example I.

FIG. 6B shows an SEM image of the double atomic layer ribbon preparedaccording to Example I.

FIG. 7A shows an atomic force microscopy (AFM) image of the doubleatomic layer ribbon prepared according to Example I.

FIG. 7B shows the height profile along the dashed arrow of FIG. 7A.

FIG. 8A shows an SEM image of the double atomic layer ribbon after fiveminutes of the UVO treatment described in Example III.

FIG. 8B shows an SEM image of the double atomic layer ribbon after eightminutes of the UVO treatment described in Example III.

FIG. 9A shows an SEM image of the example double atomic layer nanoribbonafter the etching treatment described in Example III.

FIG. 9B shows an SEM image of the double atomic layer nanoribbon afterthe etching treatment described in Example III.

FIG. 9C shows an SEM image of the double atomic layer nanoribbon afterthe etching treatment described in Example III.

FIG. 9D shows an SEM image of the double atomic layer nanoribbon afterthe etching treatment described in Example III.

FIG. 10A shows an SEM image of the double atomic layer nanoribbonprepared according to Example III.

FIG. 10B shows Auger electron spectroscopy (AES) element distributionmapping of S in the double atomic layer nanoribbon shown in FIG. 10Aprepared according to Example III.

FIG. 100 shows AES element distribution mapping of Mo in the doubleatomic layer nanoribbon shown in FIG. 10A prepared according to ExampleIII.

FIG. 10D shows AES element distribution mapping of Ni in the doubleatomic layer nanoribbon shown in FIG. 10A prepared according to ExampleIII.

FIG. 11A shows an AFM image of the double atomic layer nanoribbonprepared according to Example III.

FIG. 11B shows the height profile along the dashed arrow of FIG. 11A.

DETAILED DESCRIPTION

The present disclosure is directed to a method of preparing atomic layerribbons and nanoribbons of a TMD material. According to some aspects,the method comprises forming a double atomic layer ribbon comprising afirst monolayer and a second monolayer positioned on a surface of thefirst monolayer, and removing at least a portion of the double atomiclayer ribbon to provide an atomic layer nanoribbon of a TMD material asdescribed herein. The present disclosure is also directed to doubleatomic layer ribbons and nanoribbons, and single atomic layernanoribbons, prepared according to the methods as described herein.

As used herein, the term “ribbon” refers to an elongated structure, thatis, a structure with a length-to-width ratio of greater than 500,optionally greater than 1000. As used herein, the term “nanoribbon”refers to a ribbon with at least one dimension on the nanoscale, forexample, a ribbon having a width of between about 1 and 100 nm.

According to some aspects, the method comprises forming a double atomiclayer ribbon comprising a first monolayer and a second monolayerpositioned on a surface of the first monolayer, wherein forming thedouble atomic layer ribbon may comprise subjecting two or more precursorpowders to conditions sufficient to deposit monolayers of a TMD materialonto a substrate via chemical vapor deposition (CVD). The two or moreprecursor powders may comprise a metal oxide powder and a chalcogenpowder.

It should be understood that the metal oxide powder and the chalcogenpowder may be selected in order to provide a certain TMD material. Forexample, the metal oxide powder may comprise molybdenum dioxide (MoO₂)and the chalcogen powder may comprise sulfur (S) to provide a TMDmaterial comprising molybdenum disulfide (MoS₂). Additionally oralternatively, tungsten dioxide (WO₂) and/or tungsten trioxide (WO₃) maybe used as a metal oxide powder and/or selenium (Se) may be used as achalcogen powder such that the TMD material may comprise tungstendisulfide (WS₂) and/or molybdenum diselenide (MoSe₂) and/or tungstendiselenide (WSe₂).

According to some aspects, the two or more precursor powders mayadditionally comprise a salt powder. As used herein, the term “salt”refers to an electrically neutral ionic compound having cation(s) andanion(s). Examples of salts usefulness according to the presentdisclosure include, but are not limited to, sodium salts and potassiumsalts, such as NaBr, NaCl, KBr, KCl, and combinations thereof.

According to some aspects, the two or more precursor powders maycomprise a metal powder. The metal powder may comprise a metal that isthe same as the metal comprised by the metal oxide powder or differentfrom the metal comprised by the metal oxide powder. According to someaspects, the metal powder may comprise a transition metal such as nickel(Ni), iron (Fe), or a combination thereof.

As used herein, the term “powder” refers to particulate matter having anaverage particle size. For example, each of the two or more precursorpowders may independently comprise particulate matter having an averageparticle size of between about 1 nm and 100 μm. According to someaspects, at least one of the two or more precursor powders may compriseparticulate matter having an average particle size of between about 1and 100 nm. According to some aspects, at least one of the two or moreprecursor powders may comprise particulate matter having an averageparticle size of between about 1 and 100 μm. According to some aspects,each of the two or more precursor powders may comprise the same averageparticle size as and/or a different average particle size from theaverage particle size of another precursor powders.

According to some aspects, the substrate may comprise any inert materialsuitable for use according to the method as described herein. Examplesof substrates useful according to the present disclosure include, butare not limited to, substrates comprising or consisting of SiO₂, Si, Au,c-sapphire, fluorophlogopite mica, SrTiO₃, h-BN, or combinationsthereof.

The method may comprise subjecting the two or more precursor powders toan inert gas flow at an elevated temperature sufficient to depositmonolayers of a TMD material on a substrate via chemical vapordeposition. Example inert gasses useful according to the presentdisclosure include, but are not limited to, argon gas (Ar) and nitrogengas (N).

According to some aspects, each of the two or more precursor powders maybe subjected to the inert gas flow simultaneously or aboutsimultaneously. Alternatively, at least a first portion of the two ormore precursor powders may be subjected to the inert gas flow upstreamof at least a second portion of the two or more precursor powders toprovide a vapor atmosphere of the first portion of the two or moreprecursor powders. As used here, the term “upstream” refers to aposition closer to the source of the flow, such as the inert gas flow,in relation to a reference position. It should be understood that insome aspects, providing a first portion of the two or more precursorpowders upstream of a second portion of the two or more precursorpowders may provide an atmosphere at least partially surrounding thesecond portion of the two or more precursor powders, wherein theatmosphere comprises vapors of the first portion of the two or moreprecursor powders.

FIG. 1 shows an example of an inert gas flow 11 wherein a first portionof the two or more precursor powders 12 is provided upstream of a secondportion of the two or more precursor powders 13. According to someaspects, the first portion of the two or more precursor powders 12 maycomprise the chalcogen powder as described herein. The first portion ofthe two or more precursor powders 12 may be provided in a first tray 15.It should be understood that the term “tray” as used herein is notparticularly limited, and suitable trays include but are not limited toweigh boats, crucibles, flasks, and other vessels having any shapeand/or size that can withstand the temperature excursions of the methoddisclosed herein.

The second portion of the two or more precursor powders 13 may comprisea precursor powder mixture comprising the metal oxide powder, the metalpowder, and the salt powder as described herein. As shown in FIG. 1, thesecond portion of the two or more precursor powders 13 may be providedin a second tray 16 as described herein and may be proximal to (forexample, under, as shown in FIG. 1) a substrate 17 as described herein.However, it should be understood that the method should not be limitedto the arrangement shown in FIG. 1. For example, the second portion ofthe two or more precursor powders 13 shown in FIG. 1 may comprise themetal oxide powder and the salt powder as described herein. In thisexample, at least a surface of the substrate 17 (e.g., at least thesurface of the substrate 17 facing the second portion of the two or moreprecursor powders 13 shown in FIG. 1) may be pre-coated with the metalpowder as described herein.

According to some aspects, in the example wherein the precursor powdermixture comprises at least the metal oxide powder and the metal powderas described herein, the precursor powder mixture may have a ratio ofprecursor powders sufficient to provide double atomic layer ribbons of aTMD material as described herein. For example, the amount of the metalpowder and/or the ratio of the metal powder to the metal oxide powdermay be selected to provide metal-containing nanoparticles on thesubstrate as will be described herein. Non-limiting examples of weightratios of metal oxide powder to metal powder comprised by the precursorpowder mixture may be from about 1:0.001 to about 1:1, optionally fromabout 1:0.02 to 1:0.2.

As shown in FIG. 1, the first portion of the two or more precursorpowders 12 and the second portion of the two or more precursor powders13 may provided in a heating apparatus 14. According to some aspects,the heating apparatus may comprise a quartz tube provided with one ormore heating mechanisms. Example heating mechanisms include, but are notlimited to, heating wires, heating belts, and any mechanism capable ofproviding the elevated temperature(s) as describe herein.

For example, FIG. 1 shows a heating apparatus 14 having a first heatingmechanism comprising heating belts 18 a, 18 b, wherein the first heatingmechanism is proximal the first portion of the two or more precursorpowders 12. FIG. 1 also shows a second heating mechanism comprising aplurality of heating wires 19 a, 19 b proximal the second portion of thetwo or more precursor powders 13. However, it should be understood thatheating apparatus 14 is not necessarily limited to this arrangement. Forexample, heating belts 18 a, 18 b and/or heating wires 19 a, 19 b may bereplaced by or supplemented with other heating mechanisms as describedherein. According to some aspects, the heating apparatus 14 may beconfigured such that the first portion of the two or more precursorpowders 12 and the second portion of the two or more precursor powders13 may be independently heated, that is, such that the first portion ofthe two or more precursor powders 12 and the second portion of the twoor more precursor powders 13 are heated to different temperatures. Itshould also be understood that while FIG. 1 shows heating mechanismsprovided above and below the first portion of the two or more precursorpowders 12 and the second portion of the two or more precursor powders13, the heating mechanism(s) may be provided in any position relative tothe first portion of the two or more precursor powders 12 and the secondportion of the two or more precursor powders 13 sufficient to providethe elevated temperature(s) as described herein.

The method may comprise heating the first portion of the two or moreprecursor powders 12 to a first elevated temperature sufficient toprovide a vapor of the first portion of the two or more precursorpowders 12 as described herein. For example, in the case where the firstportion of the two or more precursor powders comprises the chalcogenpowder, the method may comprise heating the chalcogen powder to a firsttemperature sufficient to provide a chalcogen vapor atmosphere.According to some aspects, the first temperature may be between about100° C. and 300° C., and optionally about 200° C.

According to some aspects, the vapor may be provided proximal to thesecond portion of the two or more precursor powders 13. For example, asshown in FIG. 1, inert gas flow 11 may drive the vapor such that itprovides an atmosphere at least partially surrounding the second portionof two or more precursor powders 13.

The method may comprise heating the second portion of two or moreprecursor powders 13 in the presence of the vapor atmosphere to a secondelevated temperature sufficient to deposit double atomic layer ribbonsof a TMD material on a substrate via chemical vapor deposition. Forexample, as described herein, the second portion of the two or moreprecursor powders 13 may comprise a precursor powder mixture comprisingthe metal oxide powder, the metal powder, and the salt powder asdescribed herein. The method may comprise heating the second portion ofthe precursor powder mixture in the presence of the chalcogen vaporatmosphere as described herein to a second elevated temperaturesufficient to vaporize the second portion of the precursor powdermixture. In this way, double atomic layer ribbons of a TMD material maybe deposited on a substrate provided proximal to the second portion ofthe precursor powder mixture. According to some aspects, the secondtemperature may be between about 600° C. and 1000° C., optionallybetween about between about 700° C. and 900° C., and optionally betweenabout 770° C. and 850° C.

FIG. 2A shows an example double atomic layer ribbon as described herein.As shown in FIG. 2A, the double atomic layer ribbon may comprise a firstmonolayer 22 comprising a TMD material as described herein. The doubleatomic layer ribbon may further comprise a second monolayer 23comprising the TMD material, wherein the second monolayer 23 ispositioned on a surface of the first monolayer 22. The deposition of thedouble atomic layer ribbon may be at least partially guided by motion201 of a metal-containing nanoparticle 21 along the surface of thesubstrate 17. According to some aspects, the metal-containingnanoparticle may have a size on the nanoscale, for example, a particlesize of between about 1 and 100 nm. It should be understood that themetal-containing nanoparticle 21 may comprise one or more elementsprovided by the two or more precursor powders as described herein. Forexample, the metal-containing nanoparticle 21 may comprise a metal fromthe metal powder, a metal from the metal oxide powder, and/or achalcogen from the chalcogen powder. In one non-limiting example, themetal-containing nanoparticle may comprise a Ni—Mo—S nanoparticle or anFe—Mo—S nanoparticle.

According to some aspects, the metal-containing nanoparticle may have acertain element ratio. In one example, the metal-containing nanoparticlemay have a ratio of metal to chalcogen of from about 0.1:1 to about 2:1,optionally from about 0.5:1 to about 2:1, and optionally from about0.67:1 to about 1.5:1. It should be understood that the ratio of metalto chalcogen may be the ratio of metal from the metal powder tochalcogen (e.g., the ratio of Ni to S), the ratio of metal from themetal oxide powder to chalcogen (e.g., the ratio of Mo to S), or theratio of total metal to chalcogen (the ratio of (Ni+Mo) to S).

In another example, the metal-containing nanoparticle may have a firstmetal to second metal ratio of from about 0.1:1 to about 2:1, optionallyfrom about 0.5:1 to about 1.5:1. In one non-limiting example, the firstmetal may comprise the metal from the metal powder (e.g., Ni) and thesecond metal may comprise the metal from the metal oxide powder (e.g.,Mo).

As shown in FIG. 2A, the first monolayer 22 may have a first averagewidth 22 a and the second monolayer 23 may have a second average width23 a. It should be understood that the particle size of themetal-containing nanoparticle 21 may correspond with at least the secondaverage width 23 a, and in particular, the particle size of themetal-containing nanoparticle 21 may be slightly larger than the secondaverage width 23 a. It should be understood that increasing the particlesize of the metal-containing nanoparticle 21 may thus increase thesecond average width 23 a, whereas decreasing the particle size of themetal-containing nanoparticle 21 may decrease the second average width23 a.

According to some aspects, the first average width may be between about0.1 and about 100 μm, and optionally between about 1 and 10 μm.According to some aspects, the second average width may be between about0.5 and 1000 nm, and optionally between about 5 and 100 nm. According tosome aspects, the second average width may be about 10 nm, optionallyabout 20 nm, optionally about 30 nm, optionally about 40 nm, optionallyabout 50 nm, optionally about 60 nm, optionally about 70 nm, optionallyabout 80 nm, optionally about 90 nm, and optionally about 100 nm.According to some aspects, the double atomic layer ribbon may have alength of between about 1 and 1000 μm, and optionally between about 50and 500 μm.

FIG. 2B shows an example cross-sectional view of the double atomic layerribbon of FIG. 2A, including a substrate 17, a first monolayer 22, and asecond monolayer 23 positioned on a surface of the first monolayer 22.

The method may further comprise removing a portion of the double atomiclayer ribbon to provide an atomic layer nanoribbon of a TMD material asdescribed herein. According to some aspects, removing a portion of thedouble atomic layer ribbon may comprise oxidizing the portion of thedouble atomic layer ribbon to provide an oxidized portion, andseparating the oxidized portion from an un-oxidized portion to providean atomic layer nanoribbon of a TMD material.

For example, FIG. 3A shows a double atomic layer ribbon as described inrelation to FIG. 2A, including a first monolayer 22, a second monolayer23, and a metal-containing nanoparticle 21. FIG. 3B shows across-sectional view of the example shown in FIG. 3A. As shown in FIGS.3A and 3B, the first monolayer 22 comprises an unexposed portion 32(i.e., the portion of the first monolayer 22 having the second monolayer23 thereon) and an exposed portion 31 (i.e., the portion of the firstmonolayer 22 that does not have the second monolayer 23 thereon).According to some aspects, the method may comprise oxidizing the TMDmaterial comprised by the exposed portion 31 of the first monolayer 22to provide an oxidized portion, wherein the oxidized portion comprises ametal oxide material.

In some non-limiting examples, in the case wherein the TMD materialcomprised by the double atomic layer ribbon is MoS₂ or MoSe₂, the methodmay comprise oxidizing the MoS₂ or MoSe₂ of exposed portion 31 such thatit is converted to MoO₃. In another non-limiting example, in the casewherein the TMD material comprised by the double atomic layer ribbon isWS₂ or WSe₂, the method may comprise oxidizing the WS₂ or WSe₂ ofexposed portion 31 such that it is converted to WO₃. It should beunderstood that in the context of the present disclosure, oxidizingexposed portion 31 may convert exposed portion 31 to the oxidizedportion as described herein.

According to some aspects, oxidizing a portion of the double atomiclayer ribbon to provide an oxidized portion as described herein maycomprise subjecting the double atomic layer ribbon to a UV-ozone (UVO)treatment. In some non-limiting examples, the UVO treatment may compriseproviding the double atomic layer ribbon in a UVO-cleaner having a UVlight. In one example, a substrate having the double atomic layer ribbondeposited thereon (for example, by a CVD process as described herein)may be provided in a UVO-cleaner at a certain distance from the UV lightsuch that a UVO intensity is provided to the double atomic layer ribbonsufficient to oxidize the exposed portion as described herein. Accordingto some aspects, the distance between the UV light and the double atomiclayer ribbon may be between about 0.1 and 5 cm, and optionally betweenabout 0.5 and 3.2 cm. According to some aspects, the UVO treatment maybe conducted at a temperature of between about 20° C. and about 200° C.for a time of between about one minute and two hours, and optionally fora time of between about five minutes and one hour. According to someaspects, the time may be selected to oxidize at least 80% of the TMDmaterial of the exposed portion 31, optionally at least about 85%,optionally at least about 90%, optionally at least about 95%, optionallyat least about 97%, optionally at least about 98%, optionally at leastabout 99%, and optionally about 100%.

The method may further comprise etching the oxidized portion of thedouble atomic layer ribbon to provide an atomic layer nanoribbon of aTMD material. As used herein, the term “etching” refers to a subtractivemanufacturing process wherein an etching agent is used to remove one ormore substances from a surface. According to some aspects of the presentdisclosure, etching the oxidized portion of the double atomic layerribbon may comprise subjecting the double atomic layer ribbon to anetching treatment sufficient to separate the oxidized portion of thedouble atomic layer ribbon from remaining portions (e.g., un-oxidizedportions) thereof. The method may further comprise a rinsing step toremove residue etching agent.

According to some aspects, the etching agent may comprise a hydroxide,such as potassium hydroxide (KOH), sodium hydroxide (NaOH), or acombination thereof. The etching agent may be provided as a solution,for example, an aqueous solution. According to some aspects, the etchingagent may have a hydroxide concentration of between about 0.1 and 10 M,optionally between about 0.5 and 5 M, and optionally about 1 M. In onenon-limiting example, the etching treatment may comprise soaking thedouble atomic layer ribbon having at least one oxidized portion in ahydroxide solution for a time sufficient to remove the oxidized portion.The time may be, for example, between about one second and one minute,optionally between about one second and thirty seconds, and optionallyabout ten seconds. In this example, rinsing with water may be performedto remove residue etching agent.

FIG. 4A shows an example double atomic layer nanoribbon of a TMDmaterial prepared according to the present method. It should beunderstood that the double atomic layer nanoribbon shown in FIG. 4A maycorrespond with the double atomic layer ribbon of FIG. 3A wherein theexposed portion 31 has been removed as described herein. FIG. 4B shows across-sectional view of the double atomic layer nanoribbon of a TMDmaterial of FIG. 4A. It should be understood that the example doubleatomic layer nanoribbon shown in FIGS. 4A and 4B comprises the unexposedportion 32 of the first monolayer 22 and the second monolayer 23 of thedouble atomic layer ribbon shown in, for example, FIG. 3A.

It should be understood that the examples shown in FIGS. 3-4 should notnecessarily limit the present disclosure. For example, as shown in FIG.5A, the method may comprise oxidizing both the TMD material comprised bythe exposed portion 31 of the first monolayer 22 and the TMD materialcomprised by the second monolayer 23. In this example, the exposedportion 31 of the first monolayer 22 and the second monolayer 23 may becollectively referred to as an “exposed portion,” as described herein.Upon oxidation of the TMD material comprised by the exposed portion, theoxidized material comprised by the exposed portion may be collectivelyreferred to as an “oxidized portion,” as described herein. The methodmay comprise removing the oxidized portion as described herein toprovide a single atomic layer nanoribbon as shown in FIG. 5B. It shouldbe understood that the single atomic layer nanoribbon shown in FIG. 5Bcomprises the unexposed portion 32 of first monolayer 22 as shown inFIG. 5A.

The present disclosure is also directed to double atomic layer ribbonsprovided by the method described herein. According to some aspects, thedouble atomic layer ribbon may comprise a first monolayer comprising aTMD material as described herein, and a second monolayer comprising theTMD material, wherein the second monolayer is positioned on a surface ofthe first monolayer. According to some aspects, the first monolayer mayhave an average width that is greater than the average width of thesecond monolayer.

The present disclosure is also directed to double atomic layernanoribbons and single atomic layer nanoribbons provided by the methoddescribed herein.

While the aspects described herein have been described in conjunctionwith the example aspects outlined above, various alternatives,modifications, variations, improvements, and/or substantial equivalents,whether known or that are or may be presently unforeseen, may becomeapparent to those having at least ordinary skill in the art.Accordingly, the example aspects, as set forth above, are intended to beillustrative, not limiting. Various changes may be made withoutdeparting from the spirit and scope of the disclosure. Therefore, thedisclosure is intended to embrace all known or later-developedalternatives, modifications, variations, improvements, and/orsubstantial equivalents.

Thus, the claims are not intended to be limited to the aspects shownherein, but are to be accorded the full scope consistent with thelanguage of the claims, where reference to an element in the singular isnot intended to mean “one and only one” unless specifically so stated,but rather “one or more.” All structural and functional equivalents tothe elements of the various aspects described throughout this disclosurethat are known or later come to be known to those of ordinary skill inthe art are expressly incorporated herein by reference and are intendedto be encompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed as a means plus function unless the element is expresslyrecited using the phrase “means for.”

Further, the word “example” is used herein to mean “serving as anexample, instance, or illustration.” Any aspect described herein as“example” is not necessarily to be construed as preferred oradvantageous over other aspects. Unless specifically stated otherwise,the term “some” refers to one or more. Combinations such as “at leastone of A, B, or C,” “at least one of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “at least one of A,B, and C,” and “A, B, C, or any combination thereof” may be A only, Bonly, C only, A and B, A and C, B and C, or A and B and C, where anysuch combinations may contain one or more member or members of A, B, orC. Nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims.

The word “about” is used herein to mean within ±5% of the stated value,optionally within ±4%, optionally within ±3%, optionally within ±2%,optionally within ±1%, optionally within ±0.5%, optionally within ±0.1%,and optionally within ±0.01%.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the present invention, and are not intended to limit thescope of what the inventors regard as their invention nor are theyintended to represent that the experiments described below are all orthe only experiments performed. Efforts have been made to ensureaccuracy with respect to numbers used (e.g. amounts, dimensions, etc.)but some experimental errors and deviations should be accounted for.

EXAMPLES Example I: Preparation of Double Atomic Layer Ribbon

Double atomic layer MoS₂ ribbons were synthesized via a CVD methodconducted in a tube furnace system equipped with a 1″ quartz tube. Thegrowth substrate, an Si with 285 nm SiO₂ (SiO₂/Si) plate, was cleaned byacetone and isopropanol (IPA) and then placed face-down above an aluminacrucible containing a mixture of about 1.2 mg MoO₂, about 0.05 mg NaBr,and about 0.1 mg Ni powders, which was then inserted into the center ofthe quartz tube. Another crucible containing about 200 mg S powder waslocated at the upstream side of the tube, where a heating belt waswrapped. The reaction chamber was first purged with a 500 sccm (standardcubic centimeter per minute) argon gas flow for one hour. Then, thereaction was conducted at 770° C. (with a ramping rate of 40° C./min)for three minutes with 80 sccm argon gas flow. At the reactiontemperature, the temperature at the location of S powder was about 200°C. as controlled by the heating belt. After growth, the heating belt wasremoved and the furnace was cooled down naturally to room temperature.

Example II(a): Scanning Electron Microscopy Characterization of DoubleAtomic Layer Ribbon

FIG. 6A shows a scanning electrode microscopy (SEM) image the doubleatomic layer ribbon prepared according to Example I.

FIG. 6B shows another SEM image of the double atomic layer ribbonprepared according to Example I, including a first monolayer 22comprising MoS₂, a second monolayer 23 comprising MoS₂, and a Ni—Mo—Snanoparticle 21. As shown in FIG. 6B, the first monolayer 22 had a widthof about 1 μm, and the second monolayer 23 had a width of about 80 nm.The second monolayer 23 was terminated by a Ni—Mo—S nanoparticle 21,which had a diameter comparable to the width of the second monolayer 23.

Example II(b): Atomic Force Microscopy Characterization of Double AtomicLayer Ribbon

FIG. 7A shows an atomic force microscopy (AFM) image of the doubleatomic layer ribbon prepared according to Example I with topologicalinformation. FIG. 7B shows the height profile along the dashed arrow ofFIG. 7A. The height profile confirmed that the double atomic layerribbon comprised a first monolayer having a thickness of about 1 nm anda second monolayer on a surface of the first monolayer and having athickness of about 1 nm.

Example III: Preparation of Double Atomic Layer Nanoribbon

The as-grown double atomic layer MoS₂ ribbons prepared according toExample I were first treated in a UVO cleaner at 20° C. for five to tenminutes. The distance between the ribbons and UV light was about 2 cm.The sample was then subjected to an etching treatment that consisted ofsoaking the sample in a 1 M KOH aqueous solution for ten seconds andsubsequently rinsing by deionized water for ten seconds.

Example IV: Scanning Electron Microscopy Characterization of DoubleAtomic Layer Ribbon after UVO

FIGS. 8A and 8B show SEM images of the double atomic layer ribbon atdifferent points of the UVO treatment as described in Example III.

In particular, FIG. 8A shows an SEM image of the double atomic layerribbon after five minutes of the UVO treatment. As seen in FIG. 8A, thedouble atomic layer ribbon comprised a first monolayer 22 and a secondmonolayer 23 each comprising MoS₂. FIG. 8A also shows that the exposedportion 31 of the first monolayer 22 was partially converted to MoO₃ 24(light contrast).

FIG. 8B shows an SEM image of the double atomic layer ribbon after eightminutes of the UVO treatment. As seen in FIG. 8B, the double atomiclayer ribbon comprised a first monolayer 22 and a second monolayer 23,wherein the second monolayer 23 comprised MoS₂. As shown in FIG. 8B, theexposed portion 31 of the first monolayer 22 was completely converted toMoO₃ (light contrast).

Example V(a): Scanning Electron Microscopy Characterization of DoubleAtomic Layer Nanoribbon

FIG. 9A shows an SEM image of the double atomic layer nanoribbon afterthe etching treatment as described in Example III. FIG. 9A shows aNi—Mo—S nanoparticle 21 and a second monolayer 23 comprising MoS₂provided on a surface of the unexposed portion of the first monolayer(not visible).

FIG. 9B shows another SEM image of the double atomic layer nanoribbonafter the etching treatment as described in Example III. FIG. 9B shows aNi—Mo—S nanoparticle 21 and a second monolayer 23 comprising MoS₂provided on a surface of the unexposed portion of a first monolayer (notvisible). The double atomic layer nanoribbon had a width of about 10 nm.

FIG. 9C shows another SEM image of the double atomic layer nanoribbonafter the etching treatment as described in Example III. FIG. 9C shows aNi—Mo—S nanoparticle 21 and a second monolayer 23 comprising MoS₂provided on a surface of the unexposed portion of a first monolayer (notvisible). The double atomic layer nanoribbon had a width of about 20 nm.

FIG. 9D shows another SEM image of the double atomic layer nanoribbonafter the etching treatment as described in Example III. FIG. 9D shows aNi—Mo—S nanoparticle 21 and a second monolayer 23 comprising MoS₂provided on a surface of the unexposed portion of a first monolayer (notvisible). The double atomic layer nanoribbon had a width of about 50 nm.

Example V(b): Auger Electron Spectroscopy Characterization of DoubleAtomic Layer Nanoribbon

FIG. 10A shows an electron microscopy image of the double atomic layernanoribbon prepared according to Example III. As shown in FIG. 10A, thedouble atomic layer nanoribbon was terminated with a metal-containingnanoparticle 21.

FIGS. 10B-10D show Auger electron spectroscopy (AES) elementdistribution mapping of the double atomic layer nanoribbon as shown inFIG. 10A and as prepared according to Example III. In particular, FIG.10B shows AES mapping of S, FIG. 100 shows AES mapping of Mo, and FIG.10D shows AES mapping of Ni. From FIGS. 10B-10D, it was determined thatdouble atomic layer nanoribbon comprised Mo and S with a Mo:S atom ratio1:2, and that the nanoparticle comprised Ni, Mo, and S.

Example V(c): Atomic Force Microscopy Characterization of Double AtomicLayer Nanoribbon

FIG. 11A shows an AFM image of the double atomic layer nanoribbonprepared according to Example III with topological information. FIG. 11Bshows the height profile along the dashed arrow of FIG. 11A. The heightprofile confirms that the nanoribbon is a bilayer having a thickness ofabout 2 nm.

1. A method of making an atomic layer nanoribbon, the method comprising:forming a double atomic layer ribbon comprising a first monolayer and asecond monolayer on a surface of the first monolayer, wherein the firstmonolayer and the second monolayer each comprises a transition metaldichalcogenide material; oxidizing at least a portion of the firstmonolayer to provide an oxidized portion; and removing the oxidizedportion to provide an atomic layer nanoribbon comprising the transitionmetal dichalcogenide material.
 2. The method of claim 1, wherein formingthe double atomic layer ribbon comprises subjecting two or moreprecursor powders to an inert gas flow at a temperature sufficient todeposit the double atomic layer ribbon on a substrate via chemical vapordeposition, and wherein the two or more precursor powders comprise ametal oxide powder and a chalcogen powder.
 3. The method of claim 2,wherein the two or more precursor powders further comprise a metalpowder and a salt powder.
 4. The method of claim 2, wherein the metaloxide powder comprises molybdenum dioxide and the chalcogen powdercomprises sulfur.
 5. The method according to claim 3, wherein the metalpowder comprises nickel, iron, or a combination thereof.
 6. The methodof claim 1, wherein oxidizing the portion of the first monolayercomprises subjecting the double atomic layer ribbon to a UV-ozonetreatment.
 7. The method of claim 6, wherein the UV-ozone treatmentcomprises providing the double atomic layer ribbon in a UVO-cleaner. 8.The method of claim 1 further comprising oxidizing at least a portion ofthe second monolayer, wherein the oxidized portion comprises the portionof the first monolayer and the portion of the second monolayer.
 9. Themethod of claim 1, wherein removing the oxidized portion comprises anetching treatment, the etching treatment comprising subjecting theoxidized portion to an etching agent.
 10. The method of claim 9, whereinthe etching agent is selected from the group consisting of potassiumhydroxide, sodium hydroxide, and a combination thereof.
 11. The methodaccording to claim 9, wherein the etching treatment comprises subjectingthe oxidized portion to the etching agent for a time of about tenseconds.
 12. The method according to claim 1, wherein the firstmonolayer has a first average width and the second monolayer has asecond average width that is less than the first average width.
 13. Themethod according to claim 12, wherein the first average width is betweenabout 0.1 and about 100 μm.
 14. The method according to claim 12,wherein the second average width is between about 5 and 100 nm.
 15. Themethod according to claim 1, wherein the second monolayer is terminatedby a metal-containing nanoparticle.
 16. A double atomic layer ribboncomprising a first monolayer and a second monolayer on a surface of thefirst monolayer, wherein the first monolayer has a first average widthand the second monolayer has a second average width that is less thanthe first average width, and wherein the first monolayer and the secondmonolayer each comprises a transition metal dichalcogenide material. 17.The double atomic layer ribbon according to claim 16, wherein the firstaverage width is between about 0.1 and about 100 μm.
 18. The doubleatomic layer ribbon according to claim 16, wherein the second averagewidth is between about 5 and 100 nm.
 19. The double atomic layer ribbonaccording to claim 16, wherein the second monolayer is terminated by ametal-containing nanoparticle.
 20. The double atomic layer ribbonaccording to claim 16, wherein the transition metal dichalcogenidematerial comprises molybdenum disulfide.